One of the most common and versatile methods of building construction employs concrete masonry. Concrete masonry units (C.M.U.) are manufactured in various sizes, shapes, colors, and surface finishes for use in a wide variety of applications. The most common C.M.U. shapes include standard (or stretcher) units, open-ended (including bond beam, lintel, and knock-out) units, as well as single and double open-end units. The C.M.U.'s come in a number of relatively standard dimensions. Typical sizes and shapes of C.M.U.'s are illustrated in National Concrete Masonry Association (NCMA) Technical Bulletin No. TEK 2-1A (1995), the disclosure of which is incorporated herein by reference.
Other types of units besides C.M.U.'s are also commonly employed in constructing unit masonry wall systems. These include bricks (and other clay or shale units), structural tile, glass units, stone, and pre-cast stone. As used hereinafter, "unit", "masonry unit," or "block" is intended to include any construction unit utilized in building unit masonry wall systems including those units described above.
Different sizes, shapes and types of masonry units are often utilized in combination. The units are typically laid up with mortar and, optionally, with steel reinforcement, grout, and other accessories to form unit masonry wall systems of enumerable variety in size and shape. The units each often have one or more vertically extending interior cavities hereinafter referred to as "cores" so that, when multiple courses of the blocks are assembled to form a wall, the cores of the blocks are aligned to form unobstructed, continuous series of vertical spaces within the wall. Basic unit masonry wall system designs include single wythe, multiple wythe (such as cavity wall systems), and veneer systems.
A persistent problem in the design and construction of concrete unit masonry wall systems is the migration of water from the exterior of the block walls to the interior of the building. Designers and builders have tried various methods and apparatus to intercept the flow of water through masonry and direct it to the exterior of the structure. One conventional flashing approach is to install a continuous water impervious membrane at any location in block walls where the potential exists for water penetration, such as the top of walls at copings, at the base of parapets, over openings, beneath sills, over bond beams, at shelf angles, at the tops of foundations, and at the base of the wall, to serve to divert water to the exterior of the wall. The installation of flashing is, however, labor intensive, and therefore costly. In particular, conventional flashing is difficult and time consuming to properly install in block courses including rebar or other vertical reinforcement. In addition, conventional flashing is difficult to inspect since, once installed, flashing may not be evident from the exterior of the wall.
U.S. Pat. No. 5,115,614, issued to McGrath, discloses an integral flashing unit comprising a custom designed masonry block which includes a solid base and integral weep slot for collecting and directing water from the interior cavities of blocks installed in courses above the flashing unit and directing the water to the exterior of the wall. One drawback of the above-mentioned system is that it requires fabrication and shipment of a separate set of non-standard blocks for each construction job. Moreover, the nationwide acceptance and use of such specialty units is inhibited by the high costs of shipping the custom-made blocks.
U.S. Pat. No. 4,910,931, issued to Pardue, Jr., discloses a water collection and drainage system which includes a system of upper water collection pans suitable for installation in upper bond beam courses, which pans collect and direct the water through the vertical block cavities and lower block courses to another series of collection pans at a lower beam block course, which in turn direct the water to base collection pans at the lower most beam block course where the water is directed to the exterior of the wall through weeping spouts. Drawbacks to this system include the cost and complexity of installation of the multiple tiers of collection pans, as well as design limitations in the system which require installation solely in bond beam courses.